Method of making a Composite steel tubing

ABSTRACT

The specification discloses a double wall steel tubing and a method of making it which results in the production of steel tubing having a size range and wall thickness heretofore available only in a seamless tubing and possessing a uniformity of wall thickness within heretofore unattained tolerance limits. An outer welded tube is first telescoped over an inner welded tube. The two tubing sections are then mechanically bonded together as by being drawn through a sizing die in a sink pass without a mandrel or by forcing a mandrel through the inner tubing section. The composite tubing is then drawn through a second sizing die over a mandrel to produce a heavy wall tubing, equivalent in strength characteristics to single wall tubing of the seamless type.

United States Patent [191 Arntz METHOD OF MAKING A COMPOSITE STEELTUBING [75] Inventor: JohnJ. Arntz, Shelby, Ohio [73] Assignee:Copperweld Steel Company, Shelby,

Ohio

[22] Filed: Jan. 22, 1974 [21] Appl. No.: 435,526

Related U.S. Application Data [63] Continuation of Ser. No. 295,993,Oct. 10,- 1072, abandoned, which is a continuatiomin-part of Ser. No.126,633, March 22, 1971, abandoned.

[52] U.S. Cl 29/516, 29/520, 29/523, 138/1'51 [51] Int. Cl B21d 39/00,B23p 11/00 [58] Field of Search 29/516, 520, 523 X;

[56] References Cited UNITED STATES PATENTS 1,441,459 1/1923 Smalll38/5l 1,839,964 1/1932 Harvey 29/516 UX 2,063,325 12/1936 McLeod138/140 2,198,149 4/1940 Bangert 29/516 2,219,434 10/1940 White 1 129/516 UX 3,461,523 8/1969 Peehs et al 29/516 X [111 3,863,328 [451-Feb. 4, 1975 3,532,476 10/1970 Peehs et a1 29/516 X Y FOREIGN PATENTS ORAPPLICATIONS 822,983 l/l938 France 138/140 858,615 1/1952 Germany138/140 Primary Examiner-Charlie T. Moon Attorney, Agent, or Firm-Buell,Blenko & Ziesenheim [57] ABSTRACT thickness heretofore available only ina seamless tubing and possessing a uniformity of wall thickness withinheretofore unattained tolerance limits. An outer welded tube is firsttelescoped over an inner welded tube. The two tubing sections are thenmechanically bonded together as by being drawn through a sizing die in asink pass without a mandrel or by forcing a mandrel through the innertubing section. The composite tubing is then drawn through a secondsizing die over a mandrel to produce a heavy wall tubing, equivalent instrength characteristics to single wall tubing of the seamless type.

14 Claims,-4 Drawing Figures PATENTEI] FEB 41975 SHEEI 10F 2 INVENTORJohn J. Arntz METHOD OF MAKING A COMPOSITE STEEL TUBING v The presentapplication is a continuation of my prio application, Ser. No. 295,993,filed Oct. 10, 1972, now abandoned, which application in turn' is acontinuationin-part of my prior application, Ser. No. 126,633, filedMar. 22, 1971, now abandoned.

This invention relates to composite steel tubing having a degree of wallthickness not heretofore available except in steel tubing of theseamless type, and to a method of making such composite steel tubing.

Seamless tubing is produced according to presentday methods by a processinvolving heating a solid tube round to a forging temperature and thenforcing it with a rotary motion over a piercing point to form a hollowfor subsequent cold drawing. Because it is impossible to keep thepiercing point always in the exact center of the tube round during thepiercing operation, a wall thickness variation or eccentricity oftenresults. Moreover, since the tube is turning as it is being formed, aspiraling eccentricity of wall thickness may be produced. This lack ofuniformity of wall thickness may be greatly reduced or refined bysubsequent hot and cold finishing operations but the eccentricity isnever fully eliminated.

Where tolerance limits of wall thickness permit, seamless tubing may beemployed, especially in the larger size ranges. However where theapplication requires tubing having more exacting or restrictivetolerances of wall thickness, additional processing of the seamlesstubing is required, such as machining or grinding. This additionalprocessing is, however, impractical except in'relatively short sections.

An alternative process of making high-strength tubing is the colddrawing over a mandrel of electric resistance welded tubing. Thisprocess produces a tubing comparable in strength to the seamless tubingand characterized by a greater uniformity of wall thickness. Howeverthis process has its limitations in that tubing, having wall thicknessesexceeding dimensions of the order of 0.340 inch, is not presentlypractical by this method.

In accordance with the present invention, it is proposed to provide amethod for producing tubing in larger diameter ranges and greater wallthicknesses than has heretofore been attainable by known colddrawingprocesses and equal in wall thickness to tubing of the seamless type.More specifically, it is proposed to produce tubing having wallthicknesses up to twice that presently available by the cold drawingprocess by the employment of a double-wall concept in which an innertubing and an outer tubing of the same metal such as steel, aretelescoped and joined into an integral tubing. This concept has beenutilized variously with tubing of different metals for the purpose ofproviding a relatively thin layer or protective layer within or outsidea relatively thick walled tubing, where the purpose of the liner isprimarily for protection against chemical action or corrosion and notfor the addition of physical strength.

Many of the various processes by which such doublewalled tubing ofdissimilar metals are produced involve a metallurgical union or abonding with a bonding agent of the liner to the basic tubing via aheating stage. As an example, there is described in US. Pat. No.2,371,348 to M. G. Murray a process for making a composite tubing byheating telescoped sections of tubing of different metals to fuse abonding agent applied therebetween, followed by insertion of a cold barinside the inner tubing section, while still hot, to prevent separationof the outer and inner tubing sections, as cooling progresses, due tothe differing temperature coefficients of expansion of the differentmetals.

Similarly there is described in U.S. Pat. No. 2,219,434 to H. N. White aprocess for making a composite tubing having an outer tubing section ofnickel silver and an inner tubing section of sterling silver, whichprocess involves a single pass of cold drawing the telescoped tubingsections through a die and over a mandrel to effect union of the twotubing sections.

The process proposed, according to the present in vention, differs fromheretofore known methods of making composite tubing by reason of thefact that both outer and inner tubing sections are of the same metal,such as steel, and differences in the temperature coefficient ofexpansion of the telescoped tubing sections do not present a problem tobe dealt with. Moreover, absence of any requirement for a bonding agentbetween the tubing sections, simplifies the process and avoids problemsarising out of heating the assembled tubing sections.

More specifically, the proposed process involves the provision of twotubing sections of such different diameters as to enable one tubingsection to be telescoped within the other, the mechanical bonding of thetwo tubing sections by altering the diameter of one of the tubingsections relative ofthat of the other tubing section, and the colddrawing of the united tubing sections through a die and over a mandrelto size the final prodllCt.

Alteration of the diameter of one of. the tubing sections is effectedeither by cold drawing the telescoped tubing sections withoutlubrication of the use of a bonding agent therebetween, through a dieand without a mandrel to compress the outer tubing section on the innertubing section into close contact or by'cold drawing a mandrel or plugthrough the inner tubing section to expand it into contact with theouter tubing section.

The proposed process thus provides a practical method for making tubinghaving heavy wall thicknesses conforming to heretofore unattainedtolerances without requiring any special cold drawing equipment otherthan has heretofore been employed for tubing of lesser thicknesses.

The method for producing a compositetubing according to the presentinvention will be described more fully hereinafter'in connection withthe accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view, showing outer and inner tubingsections telescoped and hammered at one end preparatory to sink drawing;

FIG. 2 is a longitudinal sectional view, showing the composite tubingafter sink drawing through a die without a mandrel;

FIG. 3 is a longitudinal sectional view, showing the composite tubingafter cold drawing through a sizing die and over a mandrel; and

FIG. 4 is a longitudinal sectional view showing an alternative step tothat of FIG. 2.

As will be apparent by reference to FIG. 1, the initial step in pursuingthe process here disclosed is to select produce the ultimate productdesired. As a matter of convenience and brevity the term outsidediameter will be referred to hereafter as O.D.", the term insidediameter will be referred to as LD. and the term wall thickness will bereferred to as W.T.. Let it be assumed, for example, that two tubingsections and 11 have been selected with the following dimensions:

Tubing 0.1). |.D. W.T.

It will be noted that there is a total clearance of 0.25 inch betweenthe ID. of tubing 10 and the CD. of tubing 11, thereby enabling thetwotubings to be readily telescoped completely as shown in FIG. I, which isthe first step in the process. The tubes are nowhammered or flattened atone end with the inner tubing 1 I extending slightly outside of theouter tubing 10 and flared so as to firmly lock the two tubes 10together. Also, the

open end of the inner tubing 11 is extended an amount, such as 12 to 18inches, beyond the outer tubing 10 to compensate for the fact that theouter tube will elongate or grow in length to a greater extent than theinner tubing during the initial cold drawing stage or sink pass, now tobe described.

Referring to FIG. v2, the sink pass consists of cold drawing thehammered or flattened ends of the telescoped sections of tubing througha die 12, which in the the inner tubing. However, with the assumedtubing dimensions the OD. of the inner tubing is larger than the assumedresultant ID. of the outer tubing. Accordingly, to accomodate thesituation, the outer tubing is elongated and the inner tubingbecomessmaller in diameter. This adjustment is shown in FIG. 2, where the openend of the outer tubing 10 is shown as shifted to the right relative tothe open end of the inner tubing. At this particular stage of theprocess, it might be said that the tubing sections, theoretically atleast, form a composite tube with a 7 inch OD. and 0.75 inch W.T.

In order to avoid impairment of the mechanical bond between the ID.surface of the outer tubing and the 0D. surface of the inner tubing, nolubricant is applied to the tubing sections prior to the sink pass ofFIG. 2, except that the 0D. surface of the outer tubing is lubricated.

The next step in the process involves cold drawing the composite tubingsimultaneously through'a die 13 and over a mandrel 14, as shown in FIG.3. Preceding this cold drawing operation, the composite tubing is dippedinto a lubricant, without annealing the tubing however. Following theheretofore assumed dimensional relations of the tubing sections 10 and11, die 13 may be such as to produce a 6.5 inch 0D. for the outer tubing10 and the mandrel 14 may be such as to produce a 0.668 W.T. thusresulting in an ID. of 5.125 inches for the inner tubing section 11,which correspondingly elongates relative to the outer tubing section.

A variationof the process may be followed which involves substitutingthe step shown in FIG. 4 for the step shown in FIG. 2.

As will be apparent from the drawing, the step of FIG. 4 involvesexpansion of the inner tubing section 11 into contact with the outertubing section 10 to effect a mechanical bond therebetween. This isaccomplished in the manner illustrated by FIG. 4, that is, by pulling anappropriately sized mandrel 15 in the righthand direction through theinner tubing section 11 to expand it circumferentially into contact withthe inner diameter of the wall of the outer section 10. On the basis ofthe original tubing dimensions, the outer diameter of the inner tubingsection will be expanded 0.25 inch to match the ID. of 6.75 inches ofthe outer tubing section. Assuming no expansion of the outer tubingsection 10, the resultant O.D. forthe composite tubing would be 7.5inches. If diametrical expansion of the inner tubing section occursbeyond that necessary to effect a mechanical bond, then some lengthwiseexpansion of the inner tubing section will occur. It will be understood,therefore, that if it is desired to arrive at the same ultimate OD. forthe composite pipe while em ploying the step of FIG. 4 as for the stepof FIG. 2, a correspondingly reduced CD. of the outer tubing sectionmust be employed at the start.

A further variation of the above described process may be followed,where further improvement in the mechanical bond between the tubingsections is desired. In this variation, the ID. surface of the outertubing section is picked, that is, scored prior to the initialtelescoping of the tubing sections. This scoring operation may beaccomplished by pulling a tool through the inside diameter of the outertubing section. An example of a tool suitable for this purpose isdescribed and claimed in US. Pat. No. 3,504,513, assigned to theassignee of this application. In consequence of the scoring of theinside diameter surface of the outer tubing section, the 0D. surface ofthe inner tubing section is interlockingly impressed into the scoredindentations of the ID. surface of the outer tubing section, thusproviding a more effective mechanical bond between the two tubingsections.

In the alternative, the 0D. surface of the inner tubing section may bescored prior to the original telescoping of the tubing sections. Thiscan be accomplished incidentally to the process of making the tubingsection itself. The effect is the same as before, namely an improvementin the mechanical bond between the tubing sections of the compositetubing made in accordance with the hereinbefore describedprocess.

Tests conducted on samples of the composite tubing produced according tothe herein described process have established that in both tensile andburst strength values, the composite tubing is the equivalent inperformance to seamless tubing of similar dimensions.

It is to be understood that no limitations are intended with respect tothe sizes of tubing which may be made by the foregoing process. However,the particular utility and advantage of the process lies in producingcomposite tubing of heavy wall thickness to heretofore unattainedtolerance limits.

I claim:

l. The method of making a composite steel tubing comprising the stepsof:

a. providing two sections of welded steel tubing of substantiallyequivalent wall thickness, one of which sections has an outer diameterless than the inner diameter of the other;

b. telescoping said tubing sections and locking them together at oneend;

cold drawing said telescoped tubing sections through a die without amandrel to compress the outer tubing section onto the inner tubingsection thereby to produce a mechanical bond therebetween; and

d. cold drawing the united tubing sections through a sizing die and overa mandrel.

2. The method of making a composite steel tubing according to claim 1,wherein the sum of the wall thicknesses of the two tubing sectionsprovided exceeds 0.340 inch.

3. The method of making a composite steel tubing according to claim 1,wherein one of the tubing sections provided has its mating surfacescored prior to telescoping the tubing sections.

cording to claim 6, wherein the change in the diameter of one of saidtubing sections is accomplished by cold drawing the telescoped tubingsections through a die without a mandrel to compress the outer tubingsection onto the inner tubing section.

8. The method of making a composite steel tubing according to claim 6,wherein the change in the diameter of one of said tubing sections isaccomplished by expanding the inner one of said tubing sections.

9. The method of making a composite steel tubing according to claim 6,wherein the expansion of the inner one of said tubing sections isaccomplished by forcing 4. The method of making a composite steel tubingaccording to claim 1, wherein the outer diameter surface of the innertubing section is scored prior to telescoping the tubing sections.

5. The method of making a composite steel tubing according to claim 1,wherein the inner diameter surface of the outer tubing section is scoredprior to telescoping the tubing sections.

6. The method of making a composite steel tubing comprising the stepsof:

a. providing two sections of welded steel. tubing of substantiallyequivalent wall thickness, one of which sections has an outer diameterless than the inner diameter of the other;

b. telescoping said tubing sections and holding them together at oneend;

c. changing the diameter of one of said tubing sections so as to producea mechanical bond therebetween; and

d. cold drawing the united tubing sections through a sizing die and overa mandrel.

7. The method of making a composite steel tubing ac a mandreltherethrough.

10. The method of making a composite steel tubing according to claim 6,wherein the sum of the wall thicknesses of the two tubing sectionsprovided exceeds 0.340 inch.

11. The method of making a composite steel tubing according to claim 6,wherein one of the tubing sections provided has its mating surfacescored prior to telescoping the tubing sections.

12. The method of making a composite steel tubing according to claim 6,wherein the outer diameter surface of the inner tubing section is scoredprior to telescoping the tubing sections.

13. The method of making a composite steel tubing according to claim 6,wherein the inner diameter surface of the outer tubing section is scoredprior to telescoping the tubing sections.

14. The method of making a composite steel tubing comprising the stepsof:

a. Providing two sections of welded steel tubing of substantiallyequivalent wall thickness, one of which sections has an outer diameterless than the inner diameter of the other;

b. telescoping saidtubing sections and locking them together at one end;

0. changing the diameter of one of said tubing sections so as to producea mechanical bond therebetween; and

d. cold drawing the united tubing sections through a a mandrel.

sizing die and over

1. The method of making a composite steel tubing comprising the stepsof: a. providing two sections of welded steel tubing of substantiallyequivalent wall thickness, one of which sections has an outer diameterless than the inner diameter of the other; b. telescoping said tubingsections and locking them together at one end; cold drawing saidtelescoped tubing sections through a die without a mandrel to compressthe outer tubing section onto the inner tubing section thereby toproduce a mechanical bond therebetween; and d. cold drawing the unitedtubing sections through a sizing die and over a Mandrel.
 2. The methodof making a composite steel tubing according to claim 1, wherein the sumof the wall thicknesses of the two tubing sections provided exceeds0.340 inch.
 3. The method of making a composite steel tubing accordingto claim 1, wherein one of the tubing sections provided has its matingsurface scored prior to telescoping the tubing sections.
 4. The methodof making a composite steel tubing according to claim 1, wherein theouter diameter surface of the inner tubing section is scored prior totelescoping the tubing sections.
 5. The method of making a compositesteel tubing according to claim 1, wherein the inner diameter surface ofthe outer tubing section is scored prior to telescoping the tubingsections.
 6. The method of making a composite steel tubing comprisingthe steps of: a. providing two sections of welded steel tubing ofsubstantially equivalent wall thickness, one of which sections has anouter diameter less than the inner diameter of the other; b. telescopingsaid tubing sections and holding them together at one end; c. changingthe diameter of one of said tubing sections so as to produce amechanical bond therebetween; and d. cold drawing the united tubingsections through a sizing die and over a mandrel.
 7. The method ofmaking a composite steel tubing according to claim 6, wherein the changein the diameter of one of said tubing sections is accomplished by colddrawing the telescoped tubing sections through a die without a mandrelto compress the outer tubing section onto the inner tubing section. 8.The method of making a composite steel tubing according to claim 6,wherein the change in the diameter of one of said tubing sections isaccomplished by expanding the inner one of said tubing sections.
 9. Themethod of making a composite steel tubing according to claim 6, whereinthe expansion of the inner one of said tubing sections is accomplishedby forcing a mandrel therethrough.
 10. The method of making a compositesteel tubing according to claim 6, wherein the sum of the wallthicknesses of the two tubing sections provided exceeds 0.340 inch. 11.The method of making a composite steel tubing according to claim 6,wherein one of the tubing sections provided has its mating surfacescored prior to telescoping the tubing sections.
 12. The method ofmaking a composite steel tubing according to claim 6, wherein the outerdiameter surface of the inner tubing section is scored prior totelescoping the tubing sections.
 13. The method of making a compositesteel tubing according to claim 6, wherein the inner diameter surface ofthe outer tubing section is scored prior to telescoping the tubingsections.
 14. The method of making a composite steel tubing comprisingthe steps of: a. Providing two sections of welded steel tubing ofsubstantially equivalent wall thickness, one of which sections has anouter diameter less than the inner diameter of the other; b. telescopingsaid tubing sections and locking them together at one end; c. changingthe diameter of one of said tubing sections so as to produce amechanical bond therebetween; and d. cold drawing the united tubingsections through a sizing die and over a mandrel.